The present invention relates to a hydrofoil device (also called hydropter) with a tail unit, intended to be used on fast marine craft. It also embraces the marine craft equipped with this device. The use of hydrofoils is a technique increasingly in use in fast boats, with motor or with sail, in order to improve their performances above a certain speed, by replacing the lift of hydrostatic origin by the hydrodynamic lift of a system of submerged fins.
Two main types are currently used:
hydrofoils in which the principal bearing surfaces, generally inclined relative to the surface of the water, are only partially submerged and cross the surface, PA1 hydrofoils in which the bearing surfaces are completely submerged during normal functioning.
The first type has the advantage that it may lead to configurations where the marine craft is naturally stable relative to the surface of the water. On the other hand, it has the disadvantage of having a higher drag than the second type.
The second type on the other hand has no natural stability and must be piloted continuously. Some boats employing this type of hydrofoil are currently stabilised by an automatic pilot system acting upon rudders through the intermediary of hydraulic jacks. This leads to an expensive, heavy and complicated system.